Self-assembly of para-OH functionalized ECE-metalated pincer complexes

Abstract

a b s t r a c tVarious para-OH functionalized ECE-pincer metal complexes [MX(ECE-OH)L n ] (ECE-OH = [C 6 H 2 (CH 2 E) 2 -2,6-OH-4] À , E = NMe 2 , PPh 2 and SPh) were synthesized. The X-ray crystal structures of neutral [PdCl(SCS-OH)], [PdCl(NCN-OH)], and cationic [Pd(PCP-OH)(MeCN)](BF 4 ) are reported. The neutral halide complexes exhibit self-assembly to form polymeric chains via H-bonding involving the para-OH group as donors and the halide ligand on the metal as acceptors. Moreover, the halide ligand can be replaced by a monomeric aryloxy-O ligand leading to the formation of a covalently bonded dimer. The crystal structure of such a dimer derived from [PdI(NCN-OH)] is reported. Furthermore, these pincer-metal complexes were tethered through a carbamate linker to a siloxane functionality with the aim to be immobilized on a silica support. The crystal structure of a siloxane-functionalized [PtI(NCN-Z)] complex exemplifies how other H-bonding interactions not involving the metal-halide groupings can lead to polymeric networks as well.

PCP‐ and SCS‐Pincer Palladium Complexes Immobilized on Mesoporous Silica: Application in CC Bond Formation Reactions

“…For the PCP-pincer Pd complexes, no insertion was observed, but replacement of the halide by a h 1 -coordinated isocyanide generated the cationic, catalytically active species. Finally, this study showed that there is no need to generate a cationic palladium(II) species by prior treatment of the neutral species with, for example, Ag reagents (note that Ag halide salts are catalysts themselves) [22] for the ECE-pincer palladium species to catalyze the reaction of Eq. (1).…”

“…[23] These complexes comprise both a trialkoxysilane and an organometallic fragment covalently connected through a carbamate linker. The presence of a long, non-polar tail increases the solubility of these complexes considerably.…”

“…[21] Remarkably, this insertion takes place for both the neutral halide and the cationic aquo complexes. For the PCP-pincer Pd complexes, no insertion was observed, but replacement of the halide by a h 1 -coordinated isocyanide generated the cationic, catalytically active species.…”

“…[18] To this end, complexes 1 and 2 ( Figure 1) were synthesized [23] and subsequently immobilized on silica-based support materials. The choice of support depended on the reaction conditions, ease of functionalization of the surface groups required for attaching the catalyst, as well as on the chemical, mechanical and thermal stability of the support.…”

Highlights of 45 years of research: A personal account

“…Interesting cases of non-covalent hydrogen bonding were discovered to occur between hydrogen donor atoms present in the para-substituent Z of MX {C 6 H 2 (CH 2 NMe 2 ) 2 -2,6-Z-4} on the one end and the hydrogen accepting site X of the metal-X grouping. For example, both in the solid state and in solution MCl{C 6 H 2 (CH 2 NMe 2 ) 2 -2,6-Z-4}, M ¼ Pt, Z ¼ OH [51], forms polymers via intermolecular OH/Cl H-bonding. However, when more conformational flexibility is present in Z, as is the case for M ¼ Pd, Z ¼ CH 2 OH, a dimeric structure is formed through mutual head-to-tail OH/Cl H-bonding.…”